1. Field of the Invention
This invention relates to a new silacyclohexane compound, a method of preparing it, and a liquid crystal composition which contains it, as well as a liquid crystal display element which contains said liquid crystal composition.
2. The Prior Art
A liquid crystal display element utilizes the optical anisotropy and dielectric anisotropy of liquid crystal substances. Display methods include the TN mode (twisted nematic mode), the STN mode (super twisted nematic mode), the SBE mode (super birefringence mode), the DS mode (dynamic scattering mode), the guest-host mode, the DAP mode ("deformation of aligned phase" mode), the PD mode (polymer dispersion mode) and the OMI mode (optical mode interference mode). The most common display device has a twisted nematic structure based on the Schadt-Helfrich mode.
The properties required of the liquid crystal substance used in these liquid crystal displays are somewhat different depending on the display method. However, a wide liquid crystal temperature range and stability with regard to moisture, air, light, heat, electric fields, etc., are properties commonly required in all display methods. Furthermore, it is desirable for the liquid crystal material to have a low viscosity, and also to have a short address time, low threshold voltage and high contrast in the cell(s).
Currently, there is no single compound which satisfies all these requirements. In practice, liquid crystal mixtures are obtained by mixing several to more than ten liquid crystal compounds and latent liquid crystal compounds. Because of this, it is also important that components of a liquid crystal composition mix easily.
Of these components, the following compounds with the bicyclohexylbiphenyl structure have been known as compounds which have a particularly high T.sub.NI (nematic-isotropic transition temperature). ##STR3##
In recent years, along with the expansion of the applications of liquid crystal displays, the characteristics required of liquid crystal materials are becoming more and more advanced. In particular, there is a growing demand for materials with a nematic phase extended to a high temperature range which are to be used in conditions with a high ambient temperature such as automobile onboard use.
The nematic phase can be extended to a high temperature range by including a liquid crystal compound with a high T.sub.NI (nematic-isotropic transition temperature) as a component.